The production of water suitable for human consumption from water contaminated by one or more of microorganisms, chemicals, heavy metals and minerals is a requirement throughout the world. Many different proposals have been made for the purification of contaminated water.
A popular system in widespread use for the purification of contaminated water is a filtration based system. Such systems use a filter made from a combination of a porous media filter, activated carbon, and an ion exchange resin through which the contaminated water is passed. The filtered water is typically fed into a clean water reservoir. This type of system will reduce the levels of chlorine, lead, and pesticides. However, there are several disadvantages associated with this device.
The first disadvantage of this water purification system is that the structure of the filter provides a breeding ground for microorganisms thereby multiplying the dangers of microorganisms which may be present in very low numbers. Another disadvantage of such a water purification system is that the filter life is not measured and it is possible for the user to employ the filter beyond its useful life. A further disadvantage of such a water purification system is that oils and fuels often present in water drawn from lakes and rivers are not readily removed. Further, these oils and fuels tend to coat the filters and damage their operational life and effectiveness. Some filtration based products now incorporate a means of measuring the water volume passing though the filter and an indicator as to when to change the filter. Other filters incorporate an iodine product to minimize the risk of microbiological hazards, however, these materials often impart undesirable tastes and many are potential carcinogens.
Another popular system in use for the purification of contaminated water is a system which employs ultraviolet light for disinfection in series with a porous media and carbon filter. This type of system will reduce the levels of chlorine, lead, and pesticides and has some disinfection capability. One disadvantage with this system is that the ultraviolet light's disinfection efficacy is greatly diminished by turbidity or color in the water which can cause the filter to become contaminated by microorganisms which can readily live and breed therein thereby multiplying the danger from any microorganisms which may be present. Thus, the filter of this system also suffers from the disadvantages associated with filters of filtration based systems.
Contaminated water may also be treated to obtain drinking water by passing ozone through the water to kill microorganism contaminants such as bacteria present in the water. Various processes to treat water have been developed using combinations of filtration and ozonation.
For example, U.S. Pat. No. 5,683,576 to Olsen describes an apparatus for treating contaminated water by passing ozone through the water. In the system disclosed by Olsen, an ozone containing gas is passed through the water to be treated, until the instantaneous concentration of ozone in the head space above the water being treated reaches a predetermined level. Then, the flow of ozone through the water continues for a predetermined period of time.
The amount of ozone which must be passed through the water to purify it to any particular state will vary depending upon the initial quality of water to be treated. For example, untreated well or lake water may require a higher degree of purification than treated city water which has previously been treated to some degree.
One disadvantage of Olsen is that it can not be reliable used with such disparate types of water supply. Olsen does not monitor the total amount of ozone which passes through the water unreacted. Thus, the actual degree of treatment of the water is not measured. The system is designed only to ensure that a predetermined minimum amount of ozone passes through the system unreacted. The system makes the assumption that once the concentration of ozone reaches the predetermined level, that it does not subsequently drop below that level, or rise above that level. Further, it assumes that once the water to be. treated has been exposed to the preset ozone concentration for a predetermined time that the water is suitable for use. However, depending on the degree of contamination of the water to be treated, the time required to treat the material will vary.
In Olsen, the amount of unreacted ozone passing through the system prior to the time when the instantaneous concentration reaches the predetermined level is not measured. Further, the amount of unreacted ozone passing through the system measured during the predetermined amount of time after the predetermined instantaneous concentration is reached is not measured. Thus, the actual degree of treatment of the water is not measured.